Transfer film



United States Patent 3,494,776 TRANSFER FILM Patrick Michael Sinclair, St. Paul, and Edward R. Harrell,

White Bear Lake, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Feb. 8, 1965, Ser. No. 430,978 Int. Cl. B41m 3/12; B05c 3/20 U.S. Cl. 1173.2 3 Claims ABSTRACT OF THE DISCLOSURE A transfer film of a heat stable material such as poly- (tetrafiuoroethylene) bearing an image of a ceramic pigment admixed with a room-temperature solid thermoplastic binder such as a polyarylether-arylsulfone removable from association with the ceramic pigment at elevated temperatures without distorting the image. This image bearing film is employed for marking ceramic or glass articles by transfer of the image thereto at elevated temperatures folowed by removal of the thermoplastic binder upon further heating.

The present invention relates to the imaging of articles and especially to the application of images to articles at high temperatures. A particular aspect of our invention concerns itself with a novel film structure which can be manufactured and shipped in commerce in roll form and then unwound in use, from which preformed images are transferred to hot surfaces, e.g. in the order of 500 F. or higher.

It is a common practice to apply images, such as decorative designs and trade designations to articles made of glass, pottery, porcelain, ceramics, etc. (hereinafter collectively referred to as glass). In manufacturing such articles, it is frequently desirable to apply the images while the articles are hot. This occurs, for instance, where the image is applied as an intermediate step between two heating stages of manufacture, e.g. between the stage of initially forming or molding the article from heated materials, and a final stage where the imaged article is fired to permanently fuse the image to the article.

The temperatures at which such articles are molded and finally fired generally exceed about 500 F. However, the methods of imaging that are presently in use by the industry are not effective at such high temperatures, and therefore present manufacturing processes are burdened with having to cool the article before the image can be applied. Such cooling, if not controlled, can crack or otherwise damage some materials, and thus additional equipment for gradually and uniformly cooling is often required.

Prior methods of applying ink designs have been unsuccessful at these high temperatures for a number of reasons. For example, one of the methods presently used in the industry is silk screening, which is generally accomplished by applying an ink solution to a surface through a form of stencil. However, at temperatures much above room temperature, the solvents of the ink solution bub- 3,494,776 Patented Feb. 10, 1970 ble. The common decalcomania methods which do not employ solvents as part of the transfer step, can be applied at a somewhat higher temperature. However, heretofore known decalcomania techniques have not provided a construction that will withstand temperatures approaching, as a practical matter, those encountered in accordance with the present invention.

As far as we are aware, no one prior to our invention has provided the industry with imaging material, and techniques using the same, for suitably imaging surfaces at high temperatures in the order of above about 500 F. In general, the preferred embodiment of our invention includes a heat resistant carrier in the form of a release film with an image adhered to one face. At ambient temperatures the image is anchored to the film to permit easy unrolling and handling of the tape without displacement or loss of the image; and at the high application temperatures the image is released from the film and preferentially bonds to the hot surface without distortion and without bleeding or running of the image.

The invention and its advantages are more fully disclosed in the following detailed description and drawing, wherein:

FIGURE 1 is a perspective view of a release film illustrating a preferred embodiment of the present invention; and

FIGURE 2 is a schematic illustration of a preferred process for transferring an image from the film of FIG- URE 1 to a heated surface.

Referring to FIGURE 1, anink image 8 is formed on one face of a release film 10. The ink which forms the image in this preferred embodiment includes a high temperature ceramic pigment and a thermoplastic polymeric binder. The binder is a solid at room temperature and becomes plastic when heated. At the higher temperature and upon light pressures, the image transfers as a whole and bonds to a glass surface in preference to the carrier film. The binder is fugitive and with further heating will decompose or burn off without running or otherwise distorting the image. With the binders removed and at the high temperatures employed, the pigment fuses to the glass and forms a permanent image.

The carrier film 10 is thermally stable with said image carrying face having properties relative to the properties of the ink for releasing the image at the higher temperatures, i.e., when the binder becomes plastic. At room temperature the ink, in solid form, is suitably anchored to the release surface and will not be easily transferred, e.g., to the back of the carrier film when the film is wound in a roll 12.

The preferred process of image transfer, as illustrated in FIGURE 2, involves applying the image surface of the film to a heated surface 13 of a glass or ceramic article 14 with a continuous motion rolling action, provided by the resilient curved facing of the transfer device 16. Immediately on contact, the ink image is heated to its plastic state and transfers from the film to the glass.

Our invention will now be more specifically described with the aid of the following examples, presented in order to illustrate the invention and not, to limit it.

3 EXAMPLE 1 An ink solution was formulated from the following components.

ing Company) 2.21 Methyl isobutyl ketone solvent 4.43 Methyl ethyl ketone solvent 2.21 Cyclohexanone solvent 57.81 Cobalt oxide (pigment) 19.34

These materials were charged to a ball mill and rolled therein for a period of about 48 hours. The ball mill comprises a porcelain or earthenware jar that contains glass, steel or porcelain balls. As the jar is rolled the balls grind and pulverize the pigment to insure adequate dispersion of the pigment throughout the mixture.

The ink dispersion was removed from the ball mill and silk screened onto a film of tetrafluoroethylene (available under the trade designation Teflon from Du Pont Corp.) having a thickness of 2 mils and a 2 inch width. The film was laid on a flat surface and the silk screen laid over the film. A quantity of ink was poured along one bank of the screen and a squeegee was moved across the screen to force ink through the screen openings. The ink was thus deposited on the film to produce an ink image in accord with the design established by the openings of the screen.

The ink became dry at room temperature in a matter of minutes, but to insure complete solvent evaporation, the film was placed in an oven and heated at 225 F. for minutes.

The image carrying film was then aflixed to a silicone rubber transfer device. This device was designed for simple hand application and is similar to the device illustrated in FIGURE 2 of the drawing. As shown in the drawing, the transfer film is positioned on the device so that the image can be applied from the curved resilient facing of the device with a rolling motion. The imaged transfer film was then rolled against a 4" x 4" sample of heated ceramic (such as Pyroceram glass used by Corning Glass Works Co. in the production of its Corningware ceramic glass articles) having a temperature of about 1100 F.

During this application, the heat from the ceramic melted the thermoplastic polymers of the ink binder and caused the ink to adhere preferentially to the ceramic rather than to the carrier film to form a black image on the ceramic surface. The imaged ceramic was then fired in a kiln at a temperature of 2000" F. for 5 hours. Upon removal, the binder and fluorocarbon of the ink had sublirned or burned OE and the pigment had fused with the ceramic, resulting in a clear blue-colored imprint of the desired image.

EXAMPLE 2 In a second example, a carrier film was made by spray coating a 1 mil aluminum foil with a 60. 6% solids aqueous dispersion of Teflon in water (a latex). The coated foil was then dried in a 160 F. oven for about -20 minutes to remove the water. The discrete Teflon particles were then sintered (or fused) by placing the coated foil directly on a hot plate at 700 F. The film was then cooled and the ink solution of Example 1 was applied to the coated surface in the same manner described for Example 1. The image was dried and then transferred from the film (using the same transfer device illustrated in FIGURE 2) onto a heated glass sheet at a temperature of about 1000 F. The glass sheet was purchased on the market under the trade designation Pyrex 7740 and comprises 81% silica, 2% aluminum oxide, 13% boron oxide and small amounts of other alkali oxides.

EXAMPLE 3 An ink solution was formulated from the following components.

Material: Parts by weight A fluorocarbon of trifluorochloroethylene (available in the form of a White powder under the trade designation Kel-F 800 from Minnesota Mining and Manufacturing Company) 50 Methyl isobutyl ketone solvent Methyl ethyl ketone solvent 50 Cyclohexanone solvent 50' Cobalt oxide (pigment) 44.3

A silicone rubber having the trade designation EC- 1663-B/A, available from Minnesota Mining and Mannfacturing Company, was cast into a pad approximately Ma" thick. This silicone is formulated from the following components.

Base (B portion) material: Parts by weight OH terminated polysiloxane containing a small amount of tetra ethyl silicate (available under the trade designation RTV-60 from-General Electric Co.) 97.6 Inert polysiloxane fluid (available under the trade designation SF-69 from General Electric Co.)

The above base and accelerator are mixed at a ratio of 100 parts base to 10 parts accelerator to produce the desired silicone rubber.

The /s" pad of silicone rubber was cured on a sheet of plate glass and then stripped olf. The ink solution described above was then silk screened onto the pad in the manner described for the carrier film of Example 1. The pad, with ink image exposed, was bonded to the transfer device of Example 1 with a silicone adhesive. The transfer device with pad was placed in a 225 F. oven for 5 minutes to dry the ink. The image was then transferred from the pad to a glass surface having a temperature of 800 F. The image thus formed on the glass was clear and distinct.

Other examples have demonstrated that the carrier films of Examples 1 and 2 will transfer the ink image of Example 1 to heated glass surfaces at various temperatures from 660 F. to 1500 F., and Example 3 was successful at 400 F.

It will be noted that in Examples 1 and 2 the ink compositions include a combination of binders, namely the polyarylether-arylsulfone and the trifluorochloroethylene, whereas the ink composition of Example 3 includes only the trifiuorochloroethylene binder. The polyarylether-arylsulfone was considered to be a desirable binder at the higher temperatures employed for the first examples and the addition of trifluoroehloroethylene to the composition enhanced the wetting properties of the ink dispersion for silk screening the image onto the film.

Whatever binder employed, or whether the qualities of the pigment and binder are incorporated into a single material, the image, includin the color element, is heat convertible preferably to a permanently colored state, for example by decomposition or sublimation of a portion thereof, to an infusable character. While being essentially solid and non-tacky at ambient temperatures (to permit fiexure and transfer of the film), the image material upon being heated becomes tacky, plastic or semi-fluid, at which time the hot glass or ceramic surface and image material have an affinity for one another substantially greater than that between the image material and the carrier. In passing through this stage, however, the image material does not liquefy and run off, but is stable, and preferably, quickly adsorbed on the hot glass or ceramic surface. Insofar as we are aware, no one prior to our invention has provided in a practical sense such an assemblage of elements into a useful imaging transfer film.

Other variations are also contemplated, as for example, the film may take the form of a continuous belt where the image is silk screened onto the belt from an ink dispersion, heated to dry and remove the solvents, and then applied to glass articles all in a series of continuous operations.

We claim:

1. A transfer film having an image thereon, for imaging a hot glass or ceramic surface having a temperature in excess of 500 F., said film being handleable at ambient temperatures, and capable of being rolled up into a roll and unrolled, and then used without offset, transfer or displacement of said image, said film comprising a heat-stable polytetrafluoroethylene carrier having a smooth surface, and an image attached to said surface, said image including a ceramic pigment and a thermoplastic binder of polyarylether-arylsulfone that is essentially solid and non-tacky at ambient temperatures, and further being heat convertible without blowing and running off, said carrier having a low adhesive affinity for said image at elevated temperatures in relation to the adhesive affinity for said image of the hot surface of said glass or ceramic.

2. A composite structure containing an image, for imaging a hot surface of an article, said structure being handleable at ambient temperatures without offset, transfer or displacement of said image, said structure comprising a heat stable polymeric carrier having a smooth surface and an image attached to said surface, said image comprising a mixture of a fusible ceramic pigment and a room temperature solid, thermoplastic polymeric binder capable of removal from association with said ceramic pigment at elevated temperatures without distortion of said image, said polymeric carrier having a low adhesive afiinity for said image at elevated temperatures in relation to the adhesive aflinity for said image of the hot surface of said article.

3. A transfer film having an image thereon, for imaging a hot glass or ceramic surface, said film being handleable at ambient temperatures, and capable of being rolled up into a roll and unrolled, and then used without offset, transfer or displacement of said image, said film comprising a heat stable polymeric carrier having a smooth surface, not normally receptive to the formation of firm adhesive bonds, and an image attached to said surface, said image comprising a mixture of a fusible eeramic pigment and a thermoplastic polymeric binder essentially solid and non-tacky at ambient temperatures and capable of removal from association with said ceramic pigment at elevated temperatures without distortion of said image, said polymeric carrier having a low adhesive afiinity for said image at elevated temperatures in relation to the adhesive alfinity for said image of the hot surface of said glass or ceramic surface.

References Cited UNITED STATES PATENTS 2,502,758 4/ 1950 Short.

2,866,723 12/1958 West 117138.8 2,906,658 9/1959 Doban 117-138.8 X 2,915,416 12/1959 West 117138.8 X 3,018,188 1/1962 Nieoll 117--138.8 X 3,019,115 1/1962 Kaufmann et al. 117-1388 X 3,235,395 2/1966 Scharf 117-3.3

WILLIAM D. MARTIN, Primary Examiner H. I. GWINNELL, Assistant Examiner U.S. Cl. X.R. 

